One trend is toward the expansion of capabilities of portable communication devices. This includes the merger of formerly separate devices, such as cell phones and organizers, and the expansion of the capabilities of individual devices, such as the use of a single cell phone for more than one band of operation, e.g., AMPS and PCS bands, or the addition of voice communications, paging or other functions to phones, data terminals and other portable communication devices. As the delivery of services to communication devices and the capability of communication devices increases, the need for bandwidth of operation similarly increases. Voice communications may occur on one or more operational bands, E-mail communications on another, news information on yet another and so on.
A conflicting trend is the reduction in size of portable communication devices. A major impediment to the reduction in size is the need to include an antenna, typically in the form of a whip, helix or a combination of both, that has a length corresponding to a half or quarter of the wavelength of the operational frequency. Dual band operations typically require a switching between multiple radiators in such a whip/helix antenna structure. Expansion beyond two bands, if it can be accomplished at all, adds even more complexity. In addition, the general nature of an extendable whip with or without a helix requires the communication device to have a length which is equal or close to the length of the whip to permit its retraction and extension. The whip style antennas also suffer from reliability problems. They break, bend, and can wear from cycling, to the point where electrical contact to communication device circuits as intended becomes unreliable.
One solution to this problem has been the use of conformal patch antennas. These antennas obviate the need for an extendable whip, and in some forms can provide dual band operation. The general structure of the antenna is a patch area separated from a ground plane, generally referred to as a planar inverted F (PIFA) structure in the art. The difficulty with the patch style antenna is its size and shape. Patches in portable communication devices require a ground plane which extends slightly beyond the perimeter defined by the patch. This makes placement of the antenna, typically within the communication device, difficult to accommodate. The area of the patch is also likely to be blocked, at least partially, by a user's hand during operation.
Thus, there is a need for an improved conformal antenna for portable communication devices which meets the need for adequate radiation performance, is reliable, and does not add significantly to the dimensions of the portable device. Due to the increasing services offered by portable communication devices, such an improved antenna should be expandable to multiple bands, and should be capable of broad band operation. These and other needs are met or exceeded by the multiband antenna of the present invention.